1. Field
The present disclosure relates to a solenoid valve, and more particularly, a solenoid valve with a magnet filter in which the magnet filter is installed at one side of a bypass flow passage of the solenoid valve so that the introduction of metallic foreign substances may be prevented.
2. Description of the Related Art
A general internal combustion engine for a vehicle requires stronger torque and low rotation speed when starting to drive and requires higher rotation speed than torque so as to increase driving speed.
Thus, in order to maintain rotation of an engine at constant speed, a transmission serves to reduce rotation speed and simultaneously to increase torque using gears when the engine starts to drive and to increase rotation speed when driving speed need to be increased.
Such a transmission includes a manual transmission that a user manipulates directly a clutch and an automatic transmission that can automatically change gears using hydraulic pressure as the vehicle moves.
A solenoid valve that controls a clutch by lowly reduced control pressure (for example, 5 to 7 bar) is mainly used as an automatic transmission according to the related art.
FIG. 1 is a cross-sectional view of a solenoid valve disclosed in Korean Patent Registration No. 10-0903834 (Patent literature 1).
As illustrated in FIG. 1, a solenoid valve 10 according to the related art includes a flange 20 having a guide hollow part 21 formed therein, a feedback chamber 22, a supply chamber 23, a control chamber 24, and a discharge chamber 25 being formed in the guide hollow part 21, a spool 30 that is movably installed in the guide hollow part 21 of the flange 20 and has one or more ring-shaped grooves 31a and 31b, and a driving unit 40 that drives the spool 30.
A feedback port 22a, a supply port 23a, a control port 24a, and a discharge port 25a are formed on an outer circumferential surface of the flange 20 and are spaced apart from each other by a predetermined distance in a lengthwise direction. They communicate with the feedback chamber 22, the supply chamber 23, the control chamber 24, and the discharge chamber 25.
A plurality of land parts 32a, 32b, and 32c, of which widths are increased, are formed on an outer circumferential surface of the spool 30 and are spaced apart from each other by a predetermined distance in the lengthwise direction due to the ring-shaped grooves 31a and 31b. The plurality of land parts 32a, 32b, and 32c open/close the above-described ports 22a to 25a when the spool 30 moves due to the driving unit 40.
An external hydraulic pressure supply source (for example, a hydraulic pressure pump) is connected to the supply port 23a and supplies hydraulic pressure into the flange 20. The control port 24a is connected to a clutch (not shown) of a transmission so as to supply control pressure to the clutch (not shown) of the transmission, thereby controlling the pressure of the clutch. Pressure that remains in the solenoid valve 10 is discharged through the discharge port 25a. 
Meanwhile, the driving unit 40 includes a bobbin 42 on which coils 41 are wound, a housing 43 that surrounds an outer circumferential surface of the bobbin 42, an amateur 44 that is installed at an inner diameter part of the bobbin 42 to be movable in a vertical direction, a spindle 45 that is fixed to a center of the amateur 44 and contacts a lower end of the spool 30, a core 46 that is disposed on one end of the amateur 44, a pole 47 that is disposed on the other end of the amateur 44, and a terminal part 48 that is connected to the bobbin 42.
In the solenoid valve 10 according to the related art, no bypass flow passage is formed in the driving unit 40. Thus, the degree of precision of hydraulic pressure performance is lowered, hysteresis characteristics are irregular and thus it is difficult to precisely control hydraulic pressure when gears are shifted using a transmission.
Thus, a bypass flow passage that communicates an inner side of the driving unit 40 and an outer side of the solenoid valve 10 need to be formed. In this case, foreign substances may be introduced into the driving unit 40 via the bypass flow passage.
In particular, since the amateur 44 and the spindle 45 slide within the driving unit 40 by a magnetic force, when metallic foreign substances, such as chips as a component of the transmission or belt abrasion materials, are introduced into the driving unit 40, precise hydraulic pressure control cannot be performed due to abnormal movement of the amateur 44, and shock may occur during shifting gears or shifting gears is not performed.